Lots of romantic places to choose from depending on your interest, see website below. http://behindthebazaar.blogspot.com/2009/10/10-romantic-things-to-do-in-istanbul.html
Emirgan Park, Belgrade Forest, Camlica Hill Aya Nikolat, Buyukada, Ortakoy Square, Rumelihisarı (Rumelian Castle), Kalamış, Anadolu Kavağı, Maiden Tower, Galata Bridge
Emirgan Park, Belgrade Forest, Camlica Hill Aya Nikolat, Buyukada, Ortakoy Square, Rumelihisarı (Rumelian Castle), Kalamış, Anadolu Kavağı, Maiden Tower, Galata Bridge